Electron discharge devices for generating high frequency oscillations



y 27, 1965 D. J. WOOTTON 3,197,670

ELECTRON DISCHARGE DEVICES FOR GENERATING HIGH FREQUENCY OSCILLATIONS Filed March 16, 1959 2 Sheets-Sheet l v FIG 1 mental .D. J H00 .T bQIZ/ July 27, 1965 D. J. WOOTTON 3,197,670 ELECTRON DISCHARGE DEVICES FOR GENERATING HIGH FREQUENCY OSCILLATIONS Filed March 16. 1959 2 Sheets-Sheet 2 United States Patent 3 197 ,670 ELECTRON DISCHARE DEVICES FOR GENERAT- lNG HHGH FREQUENCY OSCHJLATIQP IS Douglas Jaques Wootton, Harrow, England, assignor to Electric 8; Musicfl Industries Limited, Hayes, England, a company of Great Britain Eiied Mar. 16, 1959, Ser. No. 799,666 Claims priority, application Great Britain, Mar. 20, 1958, 8,900/58 8 Claims. (Cl. 315-5.21)

This invention relates to electron discharge devices for genera-ting high frequency oscillations on the retarding field principle.

An electron discharge device for generating oscillations on the retarding field principle is similar to the well known reflex klystron but is distinguished therefrom in that in the latter device the reflecting electrode is disposed outside the cavity of the klystron whereas in a discharge device to which the present invention relates the reflecting electrode is disposed Within a cavity so that the reflecting electrode also has eflectively applied thereto the high frequency field set up in the cavity.

'For the purpose of tuning the resonant cavity of a retarding field oscillator it has been proposed to use the arrangement shown in FIGURE 1 of the accompanying drawings. The resonant cavity 1 has an inwardly tapered nose 2 and is coupled to an output waveguide 3, via a short length of co-axial line 4, the reflector electrode of the oscillator forming the central conductor of said co-axial line 4. The resonant cavity 1 is excited by electrons which are emitted by a cathode 5a said electrons passing through said nose 2 and being reflected by the reflector electrode so as to be collected on the wall of the cavity. The electrons excite oscillations in said cavity 1 which oscillations are transmitted via said co-axial line 4 to the waveguide 3. Tuning of the cavity 1 is effected by axially moving the reflector electrode 5 so as to vary the gap between the reflecting electrode 5 and the nose 2. Such an arrangement is disadvantageous from the point of view of ruggedness since the reflector electrode 5 must be mounted so as to be movable.

The object of the present invention is to provide an improved electron discharge device for generating high frequency oscillations whereby the aforesaid disadvantage can be reduced.

According to the invention there is provided an electron discharge device for generating high frequency oscillations on the retarding field principle comprising means for gene-rating electrons, a first body structure forming walls of a resonant cavity, an aperture in said body structure for allowing the passage of electrons from said generating means into said resonant cavity, a second body structure forming walls of a resonant tuning cavity, a co :axial transmission line coupling the first mentioned cavity to said tuning cavity for feeding high frequency oscillations set up in said first mentioned cavity to said tuning cavity, a reflector electrode in a fixed position in said first mentioned cavity for reflecting said electrons so that high frequency oscillations are set up on said first mentioned cavity by said electrons, said reflector electrode extending to said tuning cavity to form with a portion of said first body structure said coaxial transmission line, and being wholly disposed within the two body structures, means for changing the resonant frequency of said 3,197,670 Patented July 27, was

tuning cavity thereby to change the resonant frequency of said first mentioned cavity, and means for extracting said high frequency oscillations from said tuning cavity. In order that the present invention may be clearly understood and readily carried into effect, it will now be more fully described with reference to the accompanying drawings FIGURE 1 of which has already been referred to, and in which:

FEGURE 2 shows a longitudinal section of a device in accordance with one embodiment of the invention,

FIGURE 3 shows a longitudinal section of a portion of a device in accordance with another embodiment of the invention,

FIGURE 4 shows a modified portion of the device. of FIGURE 2 0r 3.

Referring to FIGURE 2 of the drawings there is shown an electron discharge device of the retarding field type in accordance with an embodiment of the invention, and which comprises an electron gun 6 including a cathode 7, an apertured electrode 8 surrounding said cathode 7 and within said cathode a heater 9. The electron gun structure is supported in the device by means of a sleeve 15 of insulating material such as ceramic having supporting longitudinal ribs, and a further insulating sleeve 11 preferably also made of ceramic. The resonant cavity of the retarding field oscillator is indicated at 12, and has, in the present embodiment, an inwardly tapering nose 13 although this may be replaced by a simple aperture in the cavity wall, for example. The cavity 12 is coupled to a tuning cavity 14 via energy feeding mean-s in the form of a short length of co-axial transmission line 15. A reflector elect-rode 16 is disposed within the cavity 12 and in a fixed position therein and a portion of said electrode 16 forms the central conductor of the co-axial transmission line 1-5 the outer conductor of which is formed by the wall of a passage leading from the cavity 12. The reflector electrode 16 is supported in a fixed position by means of an insulating annulus 17 made for example of ceramic, and which also forms a vacuum seal between the cavities 12 and 14. The electrode 16 projects into the second cavity 14 so that oscillations 'set up in the cavity 12 are fed to said second cavity 14. The cavity 14 is provided with a coupling aperture 18 from which output power can be obtained by coupling a waveguide (not shown) to the aperture 18. The electrode 16 is connected to a conductor 19 by means of which a DC.

operating potential to cause reflection of electrons can be applied to said electrode 15, the conductor 19 passing through an aperture 20 in the wall of the cavity 14. The axis of the aperture 20 is arranged to be at right angles to the axis of the reflector electrode 10 and preferably is also at right angles to the axis of the aperture 18, whereby the disposition of the lead 1 is such that the field within the cavity 14 has little coupling to the lead. The aperture 26) also accommodates a radio frequency choke 21 which surrounds the conductor 19 for the purpose of reducing the escape of high frequency energy. The choke 21 is arranged to have a length of approximately one quarter of the wavelength of the generated high frequency oscillations. For the purpose of adjusting the resonant frequency of the cavity 12, the cavity 14 is provided with tuning means the function of which will hereinafter be referred to. In the present embodiment said tuning means for the cavity 14 comprises a screw 22, engaging in the wall of the cavity 14 as shown, which can be turned to vary the length of said screw projecting in said cavity ld and thereby the width of the gap between the end of said screw 22 and the end of the reflector electrode 16 projecting into the cavity 14.

In one example of a retarding field oscillator such as the one shown in FIGURE 2 which can be employed to generate oscillations having wavelengths in the region of 3.6 ems. the resonant cavity 12 has a diameter of 0.58 inch and is 0.2 inch deep, whilst the resonant cavity 14 has a diameter of 0.75 inch and is 0.4 inch deep. The narrowestportion of the tapering nose 13 has a diameter of 0.022 inch. The reflecting end of the electrode 16 is concave the concavity having a diameter of 0.045 inch and a depth of 0.050 inch and the extremity of said reflector electrode 16 is spaced from the wall of the cavity 12 by 0.010 inch. The length of the choke 21 is arranged to be approximately 0.25 inch which is approximately one quarter of a wavelength in the operating range.

When operating the oscillator shown in FIGURE 2 having the dimensions stated above, a positive potential of 500 volts with respect to the cathode '7 may be applied to the cavities 12 and 14 and a negative potential of 150 volts-with respect to the cathode may be applied to the reflector electrode 16 via the lead 19. It is found when operating the oscillator in this manner that tuning of the cavity 12 over a range of percent can be achieved by adjusting the screw 22. The manner in which the screw 22 effects the tuning of the cavity 12 will hereinafter be more fully described.

In the embodiment of the invention shown in FIGURE 3 like reference numerals have been given to the parts in FIGURE 3 which correspond to those of FIGURE 2. The device shown in FIGURE 3 differs from that shown in FIGURE 2 in that the diameter of the portion of the reflector electrode 16 forming the inner conductor of said coaxial line is increased so that the. lower end 23 thereof forms a portion of the wall of cavity 12 and the upper end 24 forms a portion of the wall of the cavity 14. The insulating annulus 17 of FIGURE 2 is replaced by a hollow cylindrical insulating member 25 which surrounds the reflector electrode 16 as. shown andsupports the latter in its fixed position.

Movement of the screw 22 in the devices shown in F1- URES 2 and 3 has two effects. Firstly it causes a change in the length of the screw 22 projecting in the cavity 14 and so varies the resonant frequency of said cavity 14 which has the effect of changing the resonant frequency of the cavity 12. Secondly movement of the screw 22 varies the width of the gap between the end of the screw 22 and the end of the electrode 16 in the cavity 14 and inasmuch as the capacity of said gap is in series with the capacity of the gap between the reflecting end of said reflector electrode 16 and the nose 13 the variation, in the former gap width and consequent variation in the capacity thereof causes a variation of the effective gap capacity of the device and also changes the resonant frequency of the cavity 12. The first mentioned effect, is the greater except possibly when the gap between ends of the screw 22 and reflector electrode 16 in the cavity 14 is very small. Nevertheless by virtue of the second mentioned effect the tuning range of the device can be increased relatively to that resulting from the first effect alone. The resonant frequencies of the cavities 12 and 14 are similar and capable of being varied over the required bandwidth, the cavity 14 having its frequency changes made by the aforesaid mechanical tuning means and the frequency changes of the cavity 12 being made by virtue of the coupling thereof to the cavity 14. Although the resonant frequencies of the two cavities are substantially similar their dimensions in the examples shown are different owing to the different proportions of inductive and capacitative reactance making up the respective resonant cavities.

In FIGURE 3 the electron gun and associated structures of the device are not shown. These may conveniently d be similar to the electron gun and associated structure shown in FIGURE 2.

In a modification of the embodiment of the invention shown in FIGURE 2 or 3 the choke 23. may be omitted and as shown in FIGURE 4 the conductor 19 is provided with a flange 30, outside the wall of the cavity 14 and spaced therefrom by an annular member El of insulating material. The flange 30 is so dimensioned that in conjunction with the adjacent wall of the cavity 14 a high frequency short circuit is introduced for the purpose of reducing the escape of high frequency energy from said cavity 14. The diameter of the aperture 20 should be made as small as possible.

It will be appreciated that a device in accordance with the described embodiments of the invention can be made rugged since the reflector electrode is fixed in position and the only movable component is the tuning means for the second cavity 14- which can conveniently be a solid screw 22 engaging the wall of the second cavity. In alternative embodiments of the invention the screw 22 can of course e replaced by any other suitable displaceable member projecting within the cavity 14 or by means of a slug made of ferro-rnagnetic ferrite material extending into the cavity and fixed with respect thereto, the magnetic field in the cavity being changed by electromagnetic means coupled to the slug externahy of the cavity. Alternatively tuning of the cavity can be effected by providing the cavity with a distortable, such as a flexible wall.

What I claim is:

l. An electron discharge device for generating high frequency oscillations on the retarding field principle comprising means for generating electrons, a first body structure forming walls of a resonant cavity, an aperture in said body structure for allowing the passage of electrons from said generating means into said resonant cavity, a second body structure forming walls of a resonant tuning cavity, a coaxial transmission line coupling the first mentioned cavity to said tuning cavity for feeding high frequency oscillations set up in said first mentioned cavity to said tuning cavity, a reflector electrode in a fixed position in said first mentioned cavity for reflecting said electrons so that high frequency oscillations are set up in said first mentioned cavity by said electrons, said reflector electrode extending to said tuning cavity to form with a portion of said first body structure said coaxial transmission line, and being wholly disposed within the two body structures, means for changing the resonant frequency of said tuning cavity thereby to change the resonant frequency of said first mentioned cavity, and means for extracting said high frequency oscillations from said tuning cavity.

2. An electron discharge device for generating high frequency oscillations on the retarding field principle comprising means for generating electrons, a first body structure forming walls of a resonant cavity, an aperture in said body structure for allowing the passage of electrons from said generating means into said resonant cavity, a second body structure forming walls of a resonant tuning cavity, a coaxial transmission line coupling the first mentioned cavity to said tuning cavity for feeding high frequency oscillations set up in said first mentioned cavity to said tuning cavity, a reflector electrode in a fixed position in said first mentioned cavity for reflecting said electrons so that high frequency oscillations are set up in said first mentioned cavity by said electrons, said reflector electrode extending to said tuning cavity to form with a portion of said first body structure said coaxial transmission line, and being wholly disposed within the two body structures, means for changing the reso-.

nant frequency of said tuning cavity thereby to change the resonant frequency of said first mentioned cavity,

and means for extracting said high frequency oscillations from said tuning cavity, and an insulating annulus supporting said reflector electrode in said transmission line, and said insulating annulus forming a vacuum seal between said first mentioned cavity and said tuning cavity.

3. An electron discharge device for generating high frequency oscillations on the retarding field principle comprising means for generating electrons, a first body structure forming walls of a resonant cavity, an aperture in said body structure for allowing the passage of electrons from said generating means into said resonant cavity, a second body structure forming walls of a resonant tuning cavity, a coaxial transmission line coupling the first mentioned cavity to said tuning cavity for feeding high frequency oscillations set up in said first mentioned cavity to said tuning cavity, a reflector electrode in a fixed position in said first mentioned cavity for refleeting said electrons so that high frequency oscillations are set up in said first mentioned cavity by said electrons, said reflector electrode extending to said tuning cavity to form with a portion of said first body structure, said coaxial transmission line, and being wholly disposed within the two body structures, means for changing the resonant frequency of said tuning cavity thereby to change the resonant frequency of said first mentioned cavity, and means for extracting said high frequency oscillations from said tuning cavity, and a conductor for supplying operating voltage to said reflector electrode positioned to be substantially perpendicular to said reflector electrode and to extend through said second body structure.

4. An electron discharge device for generating high frequency oscillations on the retarding field principle comprising means for generating electrons, a first body structure forming walls of a resonant cavity, an aperture in said body structure for allowing the passage of electrons from said generating means into said resonant cavity, a second body structure forming walls of a resonant tuning cavity, a coaxial transmission line coupling the first mentioned cavity to said tuning cavity for feeding high frequency oscillations set up in said first mentioned cavity to said tuning cavity, a reflector electrode in a fixed position in said first mentioned cavity for reflecting said electrons so that high frequency oscillations are set up in said first mentioned cavity by said electrons, said reflector electrode extending to said tuning cavity to form with a portion of said first body structure said coaxial transmission line, and being wholly disposed Within the two body structures, means for changing the resonant frequency of said tuning cavity thereby to change the resonant frequency of said first mentioned cavity, and means for extracting said high frequency oscillations from said tuning cavity, and a conductor for supplying operating voltage to said reflector electrode positioned to be substantially perpendicular to said reflector electrode and to extend through said second body structure, and a choke surrounding said conductor, and having a. length approximately equal to one quarter of a wavelength at the frequency of the generated oscillations.

5. An electron discharge device for generating high frequency oscillations on the retarding field principle comprising means for generating electrons, a first body structure forming walls of a resonant cavity, an aperture in said body structure for allowing the passage of electrons from said generating means into said resonant cavity, a second body structure forming walls of a resonant tuning cavity, a coaxial transmission line coupling the first mentioned cavity to said tuning cavity for feeding high frequency oscillations set up in said first mentioned cavity to said tuning cavity, a reflector electrode in a fixed position in said first mentioned cavity for reflecting said electrons so that high frequency oscillations are set up in said first mentioned cavity by said electrons, said reflector electrode extending to said tuning cavity to form with a portion of said first body structure said coaxial transmission line, and being wholly disposed within the two body structures, means for changing the resonant frequency of said tuning cavity thereby to change the resonant frequency of said first mentioned cavity, and means for extracting said high frequency oscillations from said tuning cavity, and a conductor for supplying operating voltage to said reflector electrode positioned to be substantially perpendicular to said reflector electrode and to extend through an aperture in said second body structure, a flange and insulating material between said flange and the exterior of said second body structure, said flange and exterior forming radio frequency shunt circuits.

6. An electron discharge device for generating high frequency oscillations on the retarding field principle comprising means for generating electrons, a first body structure forming Walls of a resonant cavity, an aperture in said body structure for allowing the passage of electrons from said generating means into said resonant cavity, a second body structure forming Walls of a resonant tuning cavity, a coaxial transmission line coupling the first mentioned cavity to said tuning cavity for feeding high frequency oscillations set up in said first mentioned cavity to said tuning cavity, a reflector electrode in a fixed position in said firstvmentioned cavity for reflecting said electrons so that high frequency oscillations are set up in said first mentioned cavity by said electrons, said reflector electrode extending to said tuning cavity to form with a portion of said first body structure said coaxial transmission line, and being wholly disposed within the two body structures, means for changing the resonant frequency of said tuning cavity thereby to change the resonant frequency of said first mentioned cavity, and means for extracting said high frequency oscillations from said tuning cavity, and a conductor for supplying operating voltage to said reflector electrode positioned to be substantially perpendicular to said reflector electrode, and to extend through an aperture in said second body structure, the axis of said aperture being perpendicular to the axis of said reflector electrode.

7. An electron discharge device for generating high frequency oscillations on the retarding field principle comprising means for generating electrons, a first body structure forming walls of a resonant cavity, an aperture in said body structure for allowing the passage of electrons from said generating means into said resonant cavity, a second body structure forming walls of a resonant tuning cavity, a coaxial transmission line coupling the first mentioned cavity to said tuning cavity for feeding high frequency oscillations set up in said first mentioned cavity to said tuning cavity, a reflector electrode in a fixed position in said first mentioned cavity for reflecting said electrons so that high frequency oscillations are set up in said first mentioned cavity by said electrons, said reflector electrode extending to said tuning cavity to form with a portion of said first body structure said coaxial transmission line, and being wholly disposed Within the two body structures, means comprising a member projecting within said tuning cavity and displaceable to vary the projecting length thereof for changing the resonant frequency of said tuning cavity thereby to change the resonant frequency of said first mentioned cavity, and means for extracting said high frequency oscillations from said tuning cavity.

8. An electron discharge device for generating high frequency oscillations on the retarding field principle comprising means for generating electrons, a first body structure forming walls of a resonant cavity, an aperture in said body structure for allowing the passage of electrons from said generating means into said resonant cavity, a second body structure forming walls of a resonant tuning cavity, a coaxial transmission line coupling the first mentioned cavity to said tuning cavity for feeding high frequency oscillations set up in said first mentioned cavity to said tuning cavity, a reflector electrode in a fixed position in said first mentioned cavity for re fleeting said electrons so that high frequency oscillations are set up in said first mentioned cavity by said electrons, said reflector electrode extending to said tuning cavity to form with a portion of said first body structure said ccaxial transmission line, and being wholly disposed within the two body structures, means comprising a member projecting within said tuning cavity and displaceable towards and away from said reflector electrode to vary the capacity between said member and said reflecting electrode for changing the resonant frequency of said tuning cavity thereby to change the resonant frequency of said first mentioned cavity, and means for extracting said high frequency oscillations from said tuning cavity.

References Cited by the Examiner UNITED STATES PATENTS Gardner 3155.19 X Ebers 3155.2l Linder 315-521 Varian et al. 315--5.21 Gardner 315-5 .24 XR Gardner 3155.21

ARTHUR GAUSS, Primary Examiner. 

1. AN ELECTRON DISCHARGE DEVICE FOR GENERATING HIGH FREQUENCY OSCILLATIONS ON THE RETRADING FIELD PRINCIPLE COMPRISING MEANS FOR GENERATING ELECTRONS, A FIRST BODY STRUCTURE FORMING WALLS OF A RESONANT CAVITY, AN APERTURE IN SAID BODY STRUCTURE FOR ALLOWING THE PASSAGE OF ELECTRONS FROM SAID GENERATING MEANS INTO SAID RESONANT CAVITY, A SECOND BODY STRUCTURE FORMING WALLS OF A RESONANT TUNING CAVITY, A COAXIAL TRANSMISSION LINE COUPLING THE FIRST MENTIONED CAVITY TO SAID TUNING CAVITY FOR FEEDING HIGH FREQUENCY OSCILLATIONS SET UP IN SAID FIRST MENTIONED CAVITY TO SAID TURNING CAVITY, A REFLECTOR ELECTRODE IN A FIXED POSITION IN SAID FIRST MENTIONED CAVITY FOR REFLECTING SAID ELECTRONS SO THAT HIGH FREQUENCY OSCILLATIONS ARE SET UP IN SAID FIRST MENTIONED CAVITY BY SAID ELECTRONS, SAID REFLECTOR ELECTRODE EXTENDING TO SAID TUNING CAVITY TO FORM WITH A PORTION OF SAID FIRST BODY STRUCTURE SAID COAXIAL TRANSMISSION LINE, AND BEING WHOLLY DISPOSED WITHIN THE TWO BODY STRUCTURES, MEANS FOR CHANGING THE RESONANT FREQUENCY OF SAID TUNING CAVITY THEREBY TO CHANGE THE RESONANT FREQUENCY OF SAID FIRST MENTIONED CAVIT, AND MEANS FOR EXTRACTING SAID HIGH FREQUENCY OSCILLATIONS ON SAID TUNING CAVITY. 